In the midst of the Sixth Astral Era, a pact with the elementals of the Twelveswood allowed the Hyur and Elezen inhabitants of the underground city of Gelmorra to finally return to the forest above, and the nation of Gridania was born. During that same period, the warring tribes of Gyr Abania were brought together as one and the Highlander nation of Ala Mhigo was established. However, as both countries matured over the following centuries, these neighbors would not remain at peace.
About eight decades ago (around the year 1500 of the Sixth Astral Era), the reigning monarch of Ala Mhigo, King Manfred, attempted to expand his nation's influence by launching a series of large-scale campaigns into the Twelveswood. Unwilling to tolerate this intrusion, Gridania rallied its defenses, appointing the renowned lancer Vainchelon commander of its forces. The enemy general, Gylbarde, was a believer in the Fist of Rhalgr and enjoyed great popularity among the Ala Mhigans. Morale was high on both sides as the armies met on the Firesand Banks in stalemate. Though no victor emerged, Vainchelon suddenly took violently ill. He planned to fall back to land familiar to the Gridanians and ambush the Ala Mhigans as they gave chase, but died before his intentions could manifest.
Eager to prove himself to the Seedseers, Vainchelon's successor, Osbern, ordered an ambitious frontal assault on the Ala Mhigan position, but the Gridanian forces were decimated in a series of crippling defeats as Gylbarde saw through one inexperienced tactic after another. Realizing that the Ala Mhigans would be on their borders and hungry for more land should they take the Black Shroud so easily, Ishgard enlisted the aid of Ul'dah and Limsa Lominsa, uniting with Gridania to repel Gylbarde's forces. Owing to the might of this alliance, the Autumn War ended as quickly as it began, and the city-states returned to ambivalent peace. Borders were drawn and treaties signed as the city-states agreed to mutual independence on the condition that the rise of one over the others would not be tolerated.